Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
[linux/fpc-iii.git] / kernel / sched / wait.c
blob7d50f794e24802b024393d0c287fbfb1256d0b17
1 /*
2 * Generic waiting primitives.
4 * (C) 2004 Nadia Yvette Chambers, Oracle
5 */
6 #include <linux/init.h>
7 #include <linux/export.h>
8 #include <linux/sched.h>
9 #include <linux/mm.h>
10 #include <linux/wait.h>
11 #include <linux/hash.h>
13 void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
15 spin_lock_init(&q->lock);
16 lockdep_set_class_and_name(&q->lock, key, name);
17 INIT_LIST_HEAD(&q->task_list);
20 EXPORT_SYMBOL(__init_waitqueue_head);
22 void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
24 unsigned long flags;
26 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
27 spin_lock_irqsave(&q->lock, flags);
28 __add_wait_queue(q, wait);
29 spin_unlock_irqrestore(&q->lock, flags);
31 EXPORT_SYMBOL(add_wait_queue);
33 void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
35 unsigned long flags;
37 wait->flags |= WQ_FLAG_EXCLUSIVE;
38 spin_lock_irqsave(&q->lock, flags);
39 __add_wait_queue_tail(q, wait);
40 spin_unlock_irqrestore(&q->lock, flags);
42 EXPORT_SYMBOL(add_wait_queue_exclusive);
44 void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
46 unsigned long flags;
48 spin_lock_irqsave(&q->lock, flags);
49 __remove_wait_queue(q, wait);
50 spin_unlock_irqrestore(&q->lock, flags);
52 EXPORT_SYMBOL(remove_wait_queue);
56 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
57 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
58 * number) then we wake all the non-exclusive tasks and one exclusive task.
60 * There are circumstances in which we can try to wake a task which has already
61 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
62 * zero in this (rare) case, and we handle it by continuing to scan the queue.
64 static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
65 int nr_exclusive, int wake_flags, void *key)
67 wait_queue_t *curr, *next;
69 list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
70 unsigned flags = curr->flags;
72 if (curr->func(curr, mode, wake_flags, key) &&
73 (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
74 break;
78 /**
79 * __wake_up - wake up threads blocked on a waitqueue.
80 * @q: the waitqueue
81 * @mode: which threads
82 * @nr_exclusive: how many wake-one or wake-many threads to wake up
83 * @key: is directly passed to the wakeup function
85 * It may be assumed that this function implies a write memory barrier before
86 * changing the task state if and only if any tasks are woken up.
88 void __wake_up(wait_queue_head_t *q, unsigned int mode,
89 int nr_exclusive, void *key)
91 unsigned long flags;
93 spin_lock_irqsave(&q->lock, flags);
94 __wake_up_common(q, mode, nr_exclusive, 0, key);
95 spin_unlock_irqrestore(&q->lock, flags);
97 EXPORT_SYMBOL(__wake_up);
100 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
102 void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
104 __wake_up_common(q, mode, nr, 0, NULL);
106 EXPORT_SYMBOL_GPL(__wake_up_locked);
108 void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
110 __wake_up_common(q, mode, 1, 0, key);
112 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
115 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
116 * @q: the waitqueue
117 * @mode: which threads
118 * @nr_exclusive: how many wake-one or wake-many threads to wake up
119 * @key: opaque value to be passed to wakeup targets
121 * The sync wakeup differs that the waker knows that it will schedule
122 * away soon, so while the target thread will be woken up, it will not
123 * be migrated to another CPU - ie. the two threads are 'synchronized'
124 * with each other. This can prevent needless bouncing between CPUs.
126 * On UP it can prevent extra preemption.
128 * It may be assumed that this function implies a write memory barrier before
129 * changing the task state if and only if any tasks are woken up.
131 void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
132 int nr_exclusive, void *key)
134 unsigned long flags;
135 int wake_flags = 1; /* XXX WF_SYNC */
137 if (unlikely(!q))
138 return;
140 if (unlikely(nr_exclusive != 1))
141 wake_flags = 0;
143 spin_lock_irqsave(&q->lock, flags);
144 __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
145 spin_unlock_irqrestore(&q->lock, flags);
147 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
150 * __wake_up_sync - see __wake_up_sync_key()
152 void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
154 __wake_up_sync_key(q, mode, nr_exclusive, NULL);
156 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
159 * Note: we use "set_current_state()" _after_ the wait-queue add,
160 * because we need a memory barrier there on SMP, so that any
161 * wake-function that tests for the wait-queue being active
162 * will be guaranteed to see waitqueue addition _or_ subsequent
163 * tests in this thread will see the wakeup having taken place.
165 * The spin_unlock() itself is semi-permeable and only protects
166 * one way (it only protects stuff inside the critical region and
167 * stops them from bleeding out - it would still allow subsequent
168 * loads to move into the critical region).
170 void
171 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
173 unsigned long flags;
175 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
176 spin_lock_irqsave(&q->lock, flags);
177 if (list_empty(&wait->task_list))
178 __add_wait_queue(q, wait);
179 set_current_state(state);
180 spin_unlock_irqrestore(&q->lock, flags);
182 EXPORT_SYMBOL(prepare_to_wait);
184 void
185 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
187 unsigned long flags;
189 wait->flags |= WQ_FLAG_EXCLUSIVE;
190 spin_lock_irqsave(&q->lock, flags);
191 if (list_empty(&wait->task_list))
192 __add_wait_queue_tail(q, wait);
193 set_current_state(state);
194 spin_unlock_irqrestore(&q->lock, flags);
196 EXPORT_SYMBOL(prepare_to_wait_exclusive);
198 long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
200 unsigned long flags;
202 if (signal_pending_state(state, current))
203 return -ERESTARTSYS;
205 wait->private = current;
206 wait->func = autoremove_wake_function;
208 spin_lock_irqsave(&q->lock, flags);
209 if (list_empty(&wait->task_list)) {
210 if (wait->flags & WQ_FLAG_EXCLUSIVE)
211 __add_wait_queue_tail(q, wait);
212 else
213 __add_wait_queue(q, wait);
215 set_current_state(state);
216 spin_unlock_irqrestore(&q->lock, flags);
218 return 0;
220 EXPORT_SYMBOL(prepare_to_wait_event);
223 * finish_wait - clean up after waiting in a queue
224 * @q: waitqueue waited on
225 * @wait: wait descriptor
227 * Sets current thread back to running state and removes
228 * the wait descriptor from the given waitqueue if still
229 * queued.
231 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
233 unsigned long flags;
235 __set_current_state(TASK_RUNNING);
237 * We can check for list emptiness outside the lock
238 * IFF:
239 * - we use the "careful" check that verifies both
240 * the next and prev pointers, so that there cannot
241 * be any half-pending updates in progress on other
242 * CPU's that we haven't seen yet (and that might
243 * still change the stack area.
244 * and
245 * - all other users take the lock (ie we can only
246 * have _one_ other CPU that looks at or modifies
247 * the list).
249 if (!list_empty_careful(&wait->task_list)) {
250 spin_lock_irqsave(&q->lock, flags);
251 list_del_init(&wait->task_list);
252 spin_unlock_irqrestore(&q->lock, flags);
255 EXPORT_SYMBOL(finish_wait);
258 * abort_exclusive_wait - abort exclusive waiting in a queue
259 * @q: waitqueue waited on
260 * @wait: wait descriptor
261 * @mode: runstate of the waiter to be woken
262 * @key: key to identify a wait bit queue or %NULL
264 * Sets current thread back to running state and removes
265 * the wait descriptor from the given waitqueue if still
266 * queued.
268 * Wakes up the next waiter if the caller is concurrently
269 * woken up through the queue.
271 * This prevents waiter starvation where an exclusive waiter
272 * aborts and is woken up concurrently and no one wakes up
273 * the next waiter.
275 void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
276 unsigned int mode, void *key)
278 unsigned long flags;
280 __set_current_state(TASK_RUNNING);
281 spin_lock_irqsave(&q->lock, flags);
282 if (!list_empty(&wait->task_list))
283 list_del_init(&wait->task_list);
284 else if (waitqueue_active(q))
285 __wake_up_locked_key(q, mode, key);
286 spin_unlock_irqrestore(&q->lock, flags);
288 EXPORT_SYMBOL(abort_exclusive_wait);
290 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
292 int ret = default_wake_function(wait, mode, sync, key);
294 if (ret)
295 list_del_init(&wait->task_list);
296 return ret;
298 EXPORT_SYMBOL(autoremove_wake_function);
300 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
302 struct wait_bit_key *key = arg;
303 struct wait_bit_queue *wait_bit
304 = container_of(wait, struct wait_bit_queue, wait);
306 if (wait_bit->key.flags != key->flags ||
307 wait_bit->key.bit_nr != key->bit_nr ||
308 test_bit(key->bit_nr, key->flags))
309 return 0;
310 else
311 return autoremove_wake_function(wait, mode, sync, key);
313 EXPORT_SYMBOL(wake_bit_function);
316 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
317 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
318 * permitted return codes. Nonzero return codes halt waiting and return.
320 int __sched
321 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
322 int (*action)(void *), unsigned mode)
324 int ret = 0;
326 do {
327 prepare_to_wait(wq, &q->wait, mode);
328 if (test_bit(q->key.bit_nr, q->key.flags))
329 ret = (*action)(q->key.flags);
330 } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
331 finish_wait(wq, &q->wait);
332 return ret;
334 EXPORT_SYMBOL(__wait_on_bit);
336 int __sched out_of_line_wait_on_bit(void *word, int bit,
337 int (*action)(void *), unsigned mode)
339 wait_queue_head_t *wq = bit_waitqueue(word, bit);
340 DEFINE_WAIT_BIT(wait, word, bit);
342 return __wait_on_bit(wq, &wait, action, mode);
344 EXPORT_SYMBOL(out_of_line_wait_on_bit);
346 int __sched
347 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
348 int (*action)(void *), unsigned mode)
350 do {
351 int ret;
353 prepare_to_wait_exclusive(wq, &q->wait, mode);
354 if (!test_bit(q->key.bit_nr, q->key.flags))
355 continue;
356 ret = action(q->key.flags);
357 if (!ret)
358 continue;
359 abort_exclusive_wait(wq, &q->wait, mode, &q->key);
360 return ret;
361 } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
362 finish_wait(wq, &q->wait);
363 return 0;
365 EXPORT_SYMBOL(__wait_on_bit_lock);
367 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
368 int (*action)(void *), unsigned mode)
370 wait_queue_head_t *wq = bit_waitqueue(word, bit);
371 DEFINE_WAIT_BIT(wait, word, bit);
373 return __wait_on_bit_lock(wq, &wait, action, mode);
375 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
377 void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
379 struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
380 if (waitqueue_active(wq))
381 __wake_up(wq, TASK_NORMAL, 1, &key);
383 EXPORT_SYMBOL(__wake_up_bit);
386 * wake_up_bit - wake up a waiter on a bit
387 * @word: the word being waited on, a kernel virtual address
388 * @bit: the bit of the word being waited on
390 * There is a standard hashed waitqueue table for generic use. This
391 * is the part of the hashtable's accessor API that wakes up waiters
392 * on a bit. For instance, if one were to have waiters on a bitflag,
393 * one would call wake_up_bit() after clearing the bit.
395 * In order for this to function properly, as it uses waitqueue_active()
396 * internally, some kind of memory barrier must be done prior to calling
397 * this. Typically, this will be smp_mb__after_clear_bit(), but in some
398 * cases where bitflags are manipulated non-atomically under a lock, one
399 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
400 * because spin_unlock() does not guarantee a memory barrier.
402 void wake_up_bit(void *word, int bit)
404 __wake_up_bit(bit_waitqueue(word, bit), word, bit);
406 EXPORT_SYMBOL(wake_up_bit);
408 wait_queue_head_t *bit_waitqueue(void *word, int bit)
410 const int shift = BITS_PER_LONG == 32 ? 5 : 6;
411 const struct zone *zone = page_zone(virt_to_page(word));
412 unsigned long val = (unsigned long)word << shift | bit;
414 return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
416 EXPORT_SYMBOL(bit_waitqueue);
419 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
420 * index (we're keying off bit -1, but that would produce a horrible hash
421 * value).
423 static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
425 if (BITS_PER_LONG == 64) {
426 unsigned long q = (unsigned long)p;
427 return bit_waitqueue((void *)(q & ~1), q & 1);
429 return bit_waitqueue(p, 0);
432 static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
433 void *arg)
435 struct wait_bit_key *key = arg;
436 struct wait_bit_queue *wait_bit
437 = container_of(wait, struct wait_bit_queue, wait);
438 atomic_t *val = key->flags;
440 if (wait_bit->key.flags != key->flags ||
441 wait_bit->key.bit_nr != key->bit_nr ||
442 atomic_read(val) != 0)
443 return 0;
444 return autoremove_wake_function(wait, mode, sync, key);
448 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
449 * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
450 * return codes halt waiting and return.
452 static __sched
453 int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
454 int (*action)(atomic_t *), unsigned mode)
456 atomic_t *val;
457 int ret = 0;
459 do {
460 prepare_to_wait(wq, &q->wait, mode);
461 val = q->key.flags;
462 if (atomic_read(val) == 0)
463 break;
464 ret = (*action)(val);
465 } while (!ret && atomic_read(val) != 0);
466 finish_wait(wq, &q->wait);
467 return ret;
470 #define DEFINE_WAIT_ATOMIC_T(name, p) \
471 struct wait_bit_queue name = { \
472 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
473 .wait = { \
474 .private = current, \
475 .func = wake_atomic_t_function, \
476 .task_list = \
477 LIST_HEAD_INIT((name).wait.task_list), \
478 }, \
481 __sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
482 unsigned mode)
484 wait_queue_head_t *wq = atomic_t_waitqueue(p);
485 DEFINE_WAIT_ATOMIC_T(wait, p);
487 return __wait_on_atomic_t(wq, &wait, action, mode);
489 EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
492 * wake_up_atomic_t - Wake up a waiter on a atomic_t
493 * @p: The atomic_t being waited on, a kernel virtual address
495 * Wake up anyone waiting for the atomic_t to go to zero.
497 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
498 * check is done by the waiter's wake function, not the by the waker itself).
500 void wake_up_atomic_t(atomic_t *p)
502 __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
504 EXPORT_SYMBOL(wake_up_atomic_t);